The present invention relates to a compact and large-capacitance solid electrolytic capacitor. The present invention also relates to a solid electrolytic multilayer capacitor comprising a solid electrolytic capacitor using an organic material such as electrically conducting polymer or an inorganic material such as metal oxide, as a solid electrolyte.
To cope with the requirement for downsizing of electronic instruments, there is a demand for a solid electrolytic capacitor to be compact and have a large capacitance. For further reducing the size and increasing the capacitance of a solid electrolytic capacitor, it is necessary to reduce the size and increase the capacitance of the single plate solid electrolytic capacitor element housed therein itself and also to find a method capable of closely stacking the single plate elements within a limited size. In commercially available aluminum solid electrolytic capacitors, a solid electrolytic capacitor having a CV value per one unit volume of 7.0xc3x97103 Vxc2x7F/m3 is known.
Generally, a solid electrolytic capacitor contains at least one single plate capacitor element consisting of an anode part comprising a plate-like valve-acting metal having on the surface thereof an oxide dielectric film layer, and a cathode part constructed by forming a solid electrolyte layer and an electrically conducting layer sequentially on the oxide dielectric film layer. The solid electrolytic capacitor is completed by covering and sealing the periphery of the capacitor elements with a jacket resin. For the solid electrolyte layer, an organic material such as electrically conducting polymer or an inorganic material such as metal oxide is used.
In the stacking to obtain a solid electrolytic capacitor using an electrically conducting high molecular weight compound (or also called electrically conducting polymer) as the solid electrolyte, the anode part must be bent to enable spot welding after superposing respective cathode parts one on another to lie in parallel, because the cathode part of a single plate capacitor element, where a solid electrolyte layer and an electrically conducting layer are sequentially formed, is larger in the thickness than the anode part. Therefore, concentration of stress is generated in the vicinity of the boundary between the anode part and the cathode part of the single plate capacitor element and the capacitor is disadvantageously deteriorated in the capability. In order to solve this problem, various techniques have been heretofore proposed.
For example, in order to solve the difference in level between the anode part and the cathode part, a method of filling up the space between anode parts of a plurality of single plate capacitor elements with a metal plate having a thickness corresponding to the space at the time of stacking single plate capacitor elements (see, JP-A-5-205984) (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), a method of forming an insulating resin layer in the space between the anode parts and attaining the connection by a metal fine line (see, JP-A-6-29163 and JP-A-6-84716), a method of working the lead frame by dividing it into pieces corresponding to the position of each anode part (see, JP-A-4-167417) and the like are known.
As described above, for further reducing the size and increasing the capacitance of a solid electrolytic capacitor, a matter of great concern is to what degree the single plate solid electrolytic capacitor element is reduced in size and increased in capacitance and how large capacitance can be realized for the solid electrolytic capacitor by closely stacking single plate elements within a limited size (for example, a standard specification size).
More specifically, since concentration of stress is generated in the vicinity of the boundary between the anode part and the cathode part at the time of stacking single plate solid electrolytic capacitor elements, it is necessary to find a method of eliminating the difference in level and thereby preventing the concentration of stress. However, a method of eliminating the difference in level results in increase of the working step or increase in the cost such as cost for processing the material. If the working step is increased, destruction of the single plate capacitor element or deterioration of the capability increases due to the mechanical stress or the like generated during the operation, which gives rise to a problem that the yield decreases in the production of multilayer capacitors or the capacitor obtained is disadvantageously inferior in capability.
The present invention is made to solve these problems and the object of the present invention is to provide a compact and large-capacitance solid electrolytic multilayer capacitor, in which generation of the concentration of stress in the vicinity of the boundary between the anode part and the cathode part at the stacking is prevented, and thereby the capacitor is freed from the reduction of yield in the production of multilayer capacitors.
The present invention provides a solid electrolytic multilayer capacitor fabricated by stacking single plate capacitor elements. More specifically, the present invention provides:
(1) a solid electrolytic multilayer capacitor comprising a multilayer capacitor element fabricated by stacking a plurality of single plate capacitor elements each essentially consisting of an anode substrate comprising a plate-like valve-acting metal having on the surface thereof an oxide dielectric film layer, with the edge part of the anode substrate acting as the anode part; and the area exclusive of the anode part, in which a solid electrolyte layer and an electrically conducting layer are sequentially formed on the oxide dielectric film layer, acting as the cathode part; the plurality of single plate capacitor elements being stacked such that the anode parts are stacked and fixed on a lead frame in the anode side while aligning respective anode parts toward the same direction; the cathode parts are stacked and fixed on a lead frame in the cathode side through an electrically conducting adhesive layer formed thereon, to have an unfolded fan-like shape spreading out toward the distal end of the cathode part from the anode part side; and the plate-like valve-acting metal of each single plate capacitor element in the area having the solid electrolyte layer lies almost in parallel with the lead frame in the cathode side.
(2) a solid electrolytic multilayer capacitor comprising two multilayer capacitor elements each fabricated by stacking a plurality of single plate capacitor elements each essentially consisting of an anode substrate comprising a plate-like valve-acting metal having on the surface thereof an oxide dielectric film layer, with the edge part of the anode substrate acting as the anode part; and the area exclusive of the anode part, in which a solid electrolyte layer and an electrically conducting layer are sequentially formed on the oxide dielectric film layer, acting as the cathode part; the plurality of single plate capacitor elements being stacked such that the anode parts are stacked and fixed on a lead frame in the anode side while aligning respective anode parts toward the same direction; and the cathode parts are stacked and fixed on a lead frame in the cathode side through an electrically conducting adhesive layer formed thereon, to have an unfolded fan-like shape spreading out toward the distal end of the cathode part from the anode part side; the cathode parts on the electrically conducting layers of two multilayer capacitor elements being bonded and fixed through the lead frame in the cathode side to lay respective anode parts in different directions.
(3) a solid electrolytic multilayer capacitor fabricated by stacking a plurality of single plate capacitor elements each essentially consisting of an anode substrate comprising a plate-like valve-acting metal having on the surface thereof an oxide dielectric film layer, with the edge part of the anode substrate acting as the anode part; and the area exclusive of the anode part, in which a solid electrolyte layer and an electrically conducting layer are sequentially formed on the oxide dielectric film layer, acting as the cathode part; the plurality of single plate capacitor elements being stacked such that the anode parts of respective single plate capacitor elements are alternately aligned toward opposing directions; the anode parts aligned toward the same direction of alternately stacked elements are stacked and fixed on a lead frame in the anode side, and the cathode parts are stacked and fixed one on another by forming an electrically conducting adhesive layer thereon, with at least one electrically conductive adhesive layer being fixed on a lead frame in the cathode side.
(4) a solid electrolytic multilayer capacitor fabricated by stacking and fixing a plurality of single plate capacitor elements each essentially consisting of an anode substrate comprising a plate-like valve-acting metal having on the surface thereof an oxide dielectric film layer, with the edge part of the anode substrate acting as the anode part; and the area exclusive of the anode part, in which a solid electrolyte layer and an electrically conducting layer are sequentially formed on the oxide dielectric film layer, acting as the cathode part, wherein the single plate capacitor elements stacked are not the same in the length of the solid electrolyte layer. The periphery of the multilayer capacitor element is sealed by a jacket resin.
The present invention also provides a solid electrolytic capacitor in which the CV value per unit volume of one chip is 7.1xc3x97103 Vxc2x7F/m3 or more and which is fabricated by stacking the above-described multilayer solid electrolytic capacitor elements to have a required capacitor chip size for enabling the housing thereof and then sealing and molding the stacking product with a jacket resin.
In the above-described solid electrolytic multilayer capacitor, an electrically conducting adhesive layer is preferably formed in the range from the distal end of the cathode part to 80% of the cathode part length and also the multilayer capacitor element is preferably obtained by stacking the plurality of single plate capacitor elements under pressure.
Furthermore, in the above-described solid electrolytic multilayer capacitor, the single plate capacitor element is preferably a single plate capacitor element where the thickness in the distal end portion of the cathode part is larger than the thickness in the basal portion of the cathode part. More specifically, a single plate capacitor element where the end part of the anode substrate comprising a plate-like valve-acting metal having on the surface thereof an oxide dielectric film layer acts as an anode part. The area exclusive of the anode part, in which a solid electrolyte layer and an electrically conducting layer are sequentially formed on the oxide dielectric film layer, acts as a cathode part, and the thickness of the distal end portion of the cathode part is larger than the thickness of the basal portion of the cathode part. In a more preferred embodiment of the single plate capacitor element, the stacking and fixing between respective cathode parts of the plurality of single plate capacitor elements and between the cathode part and a lead frame in the cathode side is performed by means of an electrically conducting adhesive layer and the thickness of the electrically conducting adhesive layer is larger in the distal end portion of the cathode part than in the basal side of the cathode part. In the above-described solid electrolytic multilayer capacitor, the solid electrolyte layer is preferably formed using an electrically conducting polymer rather than an inorganic material.